Weakly interacting massive particles
as dark matter candidates

• Elementary particles.
• Very tiny interactions with ordinary matter.
  • They don't attract or repel ordinary particles with electrical forces.
    - and they don't emit or absorb photons.
  • They don't feel the strong nuclear force that binds protons and neutrons to make nuclei.
  • With hardly any interactions, they would be very hard to detect.
  • But it is presumed that they have the same sort of gravitational interactions as ordinary matter.
• Neutrinos almost fill the bill:
  • They don't attract or repel ordinary particles with electrical forces.
  • They don't feel the strong nuclear force that binds protons and neutrons to make nuclei.
  • With hardly any interactions, they are very hard to detect.
  • The only problem with neutrinos is that if they are really massless, then their gravitational interactions aren't strong enough.
• Of the three types of neutrinos, maybe one or two have enough mass to allow them to be an important part of the mass of the galaxy.
  • We know that the mass of the electron neutrino is very small, but our experimental knowledge of the mass of muon neutrons and tau neutrinos is quite limited.
• Maybe the WIMPS needed are a kind of particle that hasn't been discovered yet.

• The WIMPS have a spherically symmetric distribution centered on the center of the galaxy.
• They are evenly spread out, not clumped.
• They provide much of the gravitational force that holds the visible part of the galaxy together.